It has been demonstrated that the proper upper body position for a bowler requires that the shoulders remain "square". In other words, an axis passing through the shoulders, perpendicular to the direction in which the upper body is facing, should be perpendicular to the plane in which the bowling arm swings the ball and the direction in which the ball is thrown. The ball direction, as referred to here, is the direction of the ball as it leaves the bowler's hand, not the direction it may assume later, as it proceeds down the alley under the influence of its imbalance or its rotational, frictional curving forces.
Once the ball has been thrown and the arm has been fully extended in the direction of the initial ball movement, the arm should form an angle of ninety degrees with the shoulder axis. This angle is referred to as the follow-through angle and provides a quantitive measure of the squareness of the shoulder position and a substantial measure of the efficacy of the flight of the ball in rotational motion.
Relatively small deviations from the optimum 90 degree follow-through angle can have a pronounced effect on the performance of the ball. When the angle is reduced, due to a trailing bowling shoulder, the bowler cannot impart lifting force to the ball and/or the bowler may release the ball in a slightly wrong direction and miss his lane target. A reduction of this angle to 85 degrees will generally alter the angular momentum and reduce precession sufficiently to cause the ten pin to be left standing by the weaker hitting ball. An angle of 80 or 75 degrees usually reduces the hitting power of the ball enough to result in an 8-10 or 5-7 split (for a right-handed bowler).
The principal reason for the criticality of the follow-through angle is that the finger force lifting the ball is imparted at a different angle to the ball due to some error in the bowler's approach which is evidenced by the follow-through deviation, even though the finger lifting force itself remains substantially the same. A change in the angle of the finger lifting force causes the rotational axis of the ball to be shifted and alters the angular momemtum and the resulting precession. The phenomenon of precession as applied to the flight of a bowling ball is explained in the inventor's allowed U.S. patent application Ser. No. 062,359, now U.S. Pat. No. 4,233,846, entitled METHOD AND APPARATUS FOR MEASURING THE IMBALANCE OF A BOWLING BALL. The subject of the follow-through angle and its importance is discussed in greater detail in the inventor's book Balance, published in 1978 by B. T. Bowling Products of Los Angeles, Calif.
Many bowlers experience considerable difficulty in maintaining the more effective ninety degree follow-through angle. A common cause of the problem is that the bowler brings the shoulder of his bowling arm back with the ball at an early stage of the approach, thus rotating the shoulder axis relative to the lower body and setting up a much less effective shoulder axix/arm swing relationship. As the ball moves forward, the shoulder arm swing relationship is not fully corrected by moving the bowling shoulder forward to its original position, or it is not corrected at all. Often, the bowler finds it very difficult to correct this important error.
The primary objective of the present invention is to provide a device and method that will assist a bowler in maintaining a proper shoulder axis/arm swing relationship to effect a 90 degree follow-through angle.